1. Create an email address using Gmail. I gave mine an easy to remember name (4mrswhitehead).
2. When creating accounts, students will simply use this email address with a + and their name or number before the @ (firstname.lastname@example.org).
3. Gmail recognizes this as a separate email address, but all correspondence goes to the original email address. This way, students are not allowed to email using this address, but they can register and login in for websites. Also, if anyone tries to contact a student, you have record of it.
4. As far as passwords, my students all had the same password (school name and number). The email account had a different password that they did not know. You may have to confirm accounts sent as emails since your students don't have access to the account.
This works for most websites. I have found maybe one or two that do not recognize the addresses as separate accounts. It has saved me a lot of hassle and provided the ability for all of my students to enjoy great sites.